The invention relates to a multicomponent acceleration sensor.
U.S. Pat. No. 3,786,674 discloses an acceleration sensor of the generic type which consists of a plurality of individual transducers oriented such that an acceleration in a specific direction leads to an equidirectional variation of the output signals of the individual transducers. In this arrangement, the coil of each of the respective transducers is wound around a magnetostrictive iron core, so that a deformation of the iron core resulting from an acceleration (and leading by virtue of the magnetostriction to a variation in the permeability .mu..sub.r of said iron core) effects a variation in the inductance of the coil. A conclusion is drawn in evaluation electronics concerning the acceleration, from the variation in the inductance of the coil. In this process, the acceleration is transferred to the iron core by means of elements with which the acceleration sensor is supported on the object to be sensed, and which act as seismic masses. Furthermore, measures are described for screening the coil against external interferences. Moreover, it is described how the impedance can be matched in the case of a series connection of the individual transducers, so that the series connection of all individual transducers can be evaluated using only one evaluation electronics.
The disadvantage of this arrangement is that an acceleration in a direction other than that previously defined for the sensing of acceleration, likewise leads to a variation in the inductances of the coils of the individual transducers, since by virtue of mechanical strains said accelerations can also lead to deformations of the iron cores. Consequently, the accelerations can be sensed incorrectly.
German patent document DE-OS 2,432,225 A1 discloses an arrangement having a plurality of sensors for the determination of accelerations in different spacial directions in such a way that the directions of the accelerations to be determined by the individual sensors are linearly independent. However, if magnetostrictive acceleration sensors are used accelerations can still be wrongly sensed, because acceleration that deviates from the previously defined direction of the acceleration to be sensed effects mechanical strains in such a way that an acceleration is likewise sensed by the acceleration sensor.
Furthermore, another prior art device known as a multicomponent acceleration sensor is disclosed in the Symposium "Sensors, Measurement Pick-ups 1989" of the Technical Academy Esslingen (Federal Republic of Germany) from 30th May 1989 to 1st June 1989; publisher: K. W. Bonfig; chapters 2.4, 3 4; page 10.6-10.20. In that device, an acceleration sensor described as a "Piezo Beam" is constructed as active sensor element from bimorphous piezoceramic bending beams. If, in this arrangement, the acceleration sensor connected to a body to be sensed is accelerated in a direction that does not coincide with the axial direction of one of the piezoceramic bending beams, a deflection occurs due to the internal mass of the piezoceramic bending beam. This deflection leads to different charges on the front and rear (relative to the direction of acceleration) side of the piezoceramic bending beam, which are sensed using a charge amplifier which is integrated into the acceleration sensor. In this arrangement, 9 kHz is specified as the resonance frequency of the acceleration sensor. A disadvantage of this known multicomponent acceleration sensor is that a fall from a height of approximately one meter will destroy the instrument due to fracture of the piezoceramic bending beams.
It is an object of the present invention to provide a multicomponent acceleration sensor which is insensitive to mechanical stress, and at the same time to ensure, in a manner that is as simple to realize as possible, accurate detection of the acceleration to be sensed.
According to the invention, this object is achieved in a multicomponent acceleration sensor by applying to a sleeve a soft magnetic and highly magnetoelastic layer, the variation of permeability .mu..sub.r of which can be detected, for example, by means of a sensor coil. In this arrangement, the variation in permeability .mu..sub.r arises from an action of the inertial force of a seismic mass as a consequence of an acceleration. A plurality of such individual are interconnected in such a way as to produce a multicomponent acceleration sensor. A further advantage of the invention with respect to the prior art is that by virtue of the smaller seismic mass a simpler design of the acceleration sensor is possible both with regard to the weight and with regard to the dimensions of the acceleration sensor.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.